The study examines systems of medicine available in society, tracing the development of medical traditions, exploring factors in individual choice, and locating medical care systems in relation to sociocultural, economic political and historical contexts. Definitions of health and illness are considered and the importance of these issues as individual, national and world-wide concerns is examined by reviewing surveys from over thirty countries. I address the wide variety of copying styles used, past and present, to manage illness but focus on medical systems including "Western" medicine, homeopathy, chiropractic, herbalism and acupuncture. Healing systems are organized along a continuum defined at the poles by two modes of medicine--wholistic and mechanistic. I propose a general model to explain why wholistic help (e.g., chiropractic) is sought instead of or in addition to mechanistic (e.g., modern, scientific medicine) care. The theory contends that two major factors--social location and medical contingencies--affect the choice of medical care practitioners. Data from Bolivia, Canada, Colombia, India, the Ivory Coast, Jamaica, Mexico, Morocco, Sierra Leone, Taiwan, Tunisia, West Malaysia, Upper Volta and the United States are brought to bear on the hypotheses (via logit regression techniques). Referral networks (both lay and professional) are also examined using blockmodeling and discriminant techniques. The implications of these findings are discussed in relation to the social context in which medical systems operate through a consideration of the professional and societal control of practitioners.